How to use the cftime._cftime.num2date function in cftime

def test_parse_incorrect_unitstring(self):
        for datestr in ("days since2017-05-01 ", "dayssince 2017-05-01 00:00", "days snce 2017-05-01 00:00", "days_since_2017-05-01 00:00",
            "days_since_2017-05-01_00:00"):
            self.assertRaises(
                ValueError, cftime._cftime._dateparse, datestr, 'standard')

            self.assertRaises(
                ValueError, cftime._cftime.num2date, 1, datestr, 'standard')

            self.assertRaises(
                ValueError, cftime._cftime.date2num, datetime(1900, 1, 1, 0), datestr, 'standard')

def test_parse_incorrect_unitstring(self):
        for datestr in ("days since2017-05-01 ", "dayssince 2017-05-01 00:00", "days snce 2017-05-01 00:00", "days_since_2017-05-01 00:00",
            "days_since_2017-05-01_00:00"):
            self.assertRaises(
                ValueError, cftime._cftime._dateparse, datestr)

            self.assertRaises(
                ValueError, cftime._cftime.num2date, 1, datestr)

            self.assertRaises(
                ValueError, cftime._cftime.date2num, datetime(1900, 1, 1, 0), datestr)